Accelerometers may be used to detect the acceleration rate of moving objects, such as cars, airplanes, or the like. FIG. 1A illustrates a top view of a convention single-axis accelerometer 100. A cross-sectional view of accelerometer 100 is shown in FIG. 1B, wherein the cross-sectional view is taken along a plane crossing line 1B-1B in FIG. 1A. In the center of accelerometer 100, there is proof-mass 102 that has a relatively great mass. Springs 104 support proof-mass 102 (also refer to FIG. 1B), and allow proof-mass 102 to move in the x directions (either +x or −x directions). Proof-mass 102 is supported by springs 104. Proof-mass 102 and conductive components 108 are both conductive, and hence form capacitors. If accelerometer 100 does not experience acceleration, proof-mass 102 is located at a balance point. When accelerometer 100 does experience acceleration in one of the +x and −x directions, proof-mass 102 will move to the direction opposite to the acceleration direction. The capacitance between proof-mass 102 and conductive components 108 changes accordingly. By measuring the change in the capacitance, the acceleration rate and the acceleration direction (+x direction or −x direction) may be calculated.
FIG. 2 illustrates a top view of a double-axis accelerometer, which may move in both x (+x and −x) directions and y (+y and −y) directions. The mechanism is similar to the mechanism of the single-axis accelerometer, except the springs are also formed in the y directions (+y and −y directions), and the corresponding capacitances reflecting the movement of proof-mass 102 in the y directions is also measured.